Understanding Sacroiliac Joint Pain
The sacroiliac (SI) joint is the largest axial joint in the body, connecting the sacrum to the ilium of the pelvis. It transmits all upper body load to the lower extremities during standing and walking. Despite minimal movement (2–4° rotation, 2 mm translation), the SIJ is a significant pain generator responsible for 15 to 30% of chronic low back pain cases.
Causes of SI Joint Dysfunction
| Cause | Examples |
|---|---|
| Pregnancy & postpartum | Relaxin-induced ligamentous laxity, altered gait |
| Acute trauma | Fall, motor vehicle accident, heavy lifting |
| Leg length discrepancy | Asymmetric loading of SIJ surfaces |
| Hip or lumbar pathology | Altered biomechanics increasing SIJ stress |
| Inflammatory arthritis | Ankylosing spondylitis, psoriatic arthritis |
| Post-lumbar fusion | Increased compensatory motion at SIJ |
| Deconditioning | Weakened pelvic stabilisers |
Diagnosing SI Joint Pain: Clinical Tests
A physiotherapist typically uses a cluster of provocation tests:
- FABER Test (Flexion, ABduction, External Rotation) — SIJ pain reproduced in the posterior pelvis
- Gaenslen's Test — posterior shear force on the SIJ
- Posterior Shear/Thigh Thrust — most sensitive for SIJ involvement
- Distraction Test — anterior gapping of the SIJ
- Compression Test — lateral compression of the iliac crests
A positive cluster of three or more tests has sensitivity above 85% for SIJ involvement.
SI Joint Pain Exercises: 6 Key Movements
1. Posterior Pelvic Tilt
Lie on your back with knees bent. Gently flatten the lower back against the floor by contracting the abdominals. Hold 5 seconds, 10 repetitions. This activates transversus abdominis without stressing the SIJ.
2. Bridge Exercise
Lie on your back, feet hip-width apart. Lift the pelvis off the floor maintaining neutral pelvis symmetry. Hold 3 seconds, lower slowly. 3 sets × 12 repetitions. Avoid arching the lower back at the top.
3. Clamshell
Lie on your side, hips and knees bent. Open the top knee toward the ceiling without allowing the pelvis to rotate. 3 sets × 15 reps. Strengthens gluteus medius — the primary SIJ stabiliser.
4. Standing Hip Abduction
Stand on one leg near a wall for support. Lift the opposite leg laterally to 30°, hold 2 seconds, lower. 3 sets × 12 reps. Challenges SIJ stability in a functional weight-bearing position.
5. Modified Plank (Shortened Lever)
Kneel on all fours, arms straight. Extend one leg back at a time, maintaining a neutral pelvis. Progress to full plank when able. Builds deep core stability without excessive SIJ loading.
6. Dead Bug
Lie on your back, arms and legs raised to 90°. Slowly lower one arm and the opposite leg toward the floor, keeping the lower back flat. Alternate sides. 3 sets × 8 reps per side.
Sitting Positions for SI Joint Pain
| Sitting Position | Effect on SIJ |
|---|---|
| Symmetric sit (equal weight both sides) | Neutral — recommended |
| Crossed leg (one leg over other) | Increases SIJ shear — avoid |
| Slumped posture | Increases posterior SIJ strain |
| Wedge cushion (thin edge back) | Reduces posterior shear — helpful |
| Frequent position changes | Prevents sustained loading — recommended |
Sleeping Positions for SI Joint Pain
- Best position: Side-lying with a pillow between the knees to maintain pelvic alignment
- Avoid: Sleeping on the stomach (creates lumbar hyperextension and SIJ rotation)
- Acceptable: Back-lying with a small pillow under the knees to reduce SIJ posterior stress
SI Joint Belts
SI joint support belts worn at the level of the posterior superior iliac spines (PSIS) provide external compression and reduce joint laxity. They are particularly useful during pregnancy, postpartum, and the early stages of conservative rehabilitation. Belts should be worn during activity, not during sleep.
When to Seek Professional Help
Consult a physiotherapist if:
- Pain persists beyond 6 to 8 weeks of conservative management
- Pain is bilateral or accompanied by skin changes, eye inflammation, or morning stiffness exceeding 30 minutes (possible ankylosing spondylitis)
- Neurological symptoms develop (leg weakness, numbness, bladder changes)
For related guides, see lower back pain self-care and lumbar spondylosis exercises.
References
- Laslett M et al. Diagnosis of sacroiliac joint pain. Manual Therapy. 2005.
- Vleeming A et al. European guidelines for the diagnosis and treatment of pelvic girdle pain. European Spine Journal. 2008.
- Pool-Goudzwaard AL et al. Insufficient lumbopelvic stability: a clinical, anatomical and biomechanical approach to 'a-specific' low back pain. Manual Therapy. 1998.